self-rising flour

I was at my mom's home attempting to use overripe bananas in a banana bread, when I got to the dry ingredients and realized my mom was out of flour (she's not a big baker). For some reason, she had self-rising flour, so i left out the added leavener and just went with the 1 1/4 c self rising flour. The flavor was off and the texture was much fluffier than usual. Can anyone explain the science behind this.

Just some logical guesses: Off flavors could be anything: age; storage conditions; type of leavening in the SR flour; etc. Fluffiness could be because SR flours likely are low protein, as SR flours are more likely substitutes for cake flour than for AP or bread flour.

Four guesses: Old flour = rancid flour = off flavor. Self-rising flour typically has salt added to it in addition to the leavening so that might have been a factor in both flavor and texture. The flour could simply have had more or less leavening than your recipe calls for. Bleaching changes flour to a discernible extent and most self-riding flours are bleached.